With the development of data storage techniques, various data storage devices now provide users with higher and higher data storage capacity, and also their data access speed has been increased greatly. Besides the increase of data storage capacity, users also impose greater and greater demands on data reliability and response time of storage systems.
So far multi-level caching techniques have been developed to cache recently accessed data. At this point, recently accessed data may reside in a buffer device with a high speed; when an access request with respect to these data is received again, data may be directly provided from the buffer device, rather than being loaded from an underlying storage device with a low speed. However, a data write request might move or modify accessed data, which will be processed as new data. At this point, the hit rate of data in the buffer device will be reduced, and further the buffer device cannot fulfill desired functions.